@guozhihua12 I'm having a little trouble reproducing this. Would you mind updating with the full code you're using for a repo? For instance, I'm not exactly sure how you are defining api and it doesn't seem to be something with direct documentation.

To try to reproduce, I used a file like this

from marshmallow import Schema, fields
import hug

class TestingSchema(Schema):
    a = fields.Integer(required=True)
    b = fields.Integer(required=True)
    c = fields.Integer()

@hug.route.post('/test')
def test_validation(body: TestingSchema()):
    return True, '', body

and then used POST requests like this

➜  hug-examples curl -X POST localhost:8000/test -d "a=1&b=2&c=3"
[true, "", {"b": 2, "a": 1, "c": 3}]
➜  hug-examples curl -X POST localhost:8000/test
{"errors": {"body": {"_schema": ["Invalid input type."]}}}